Approximately 65% of service members seriously injured in Iraq and Afghanistan sustain injuries to their extremities. Many of these individuals experience muscle tissue loss and/or nerve injury, resulting in the loss of limb function or substantial reduction thereof. Injuries to the lower leg can be particularly devastating due to the critical importance of the ankle in providing support for body position, and in propelling the body forward economically during common functions such as level-ground walking and the ascent and descent of stairs and slopes.
Increasingly, robotic technology is employed in the treatment of individuals suffering from physical disability, either for the advancement of therapy tools or as permanent assistive devices. An important class of robotic devices provides therapy to the arms of stroke patients. Additionally, lower-extremity robotic devices have been developed for the enhancement of locomotor function. Although decades of research has been conducted in the area of active permanent assistive devices for the treatment of lower-extremity pathology, there devices are not designed to produce a biomimetic response, generally described in terms of joint torque, joint angle, and other related parameters as observed in a human not having substantial muscle tissue injury and not using any device to assist in ambulation. Therefore, the robotic devices usually result in unnatural ambulation and may even cause significant discomfort to the wearer. As such, many commercially available ankle-foot orthoses remain passive and non-adaptive to the wearer even today.
These passive devices cannot adequately address two major complications of anterior muscle weakness, which include slapping of the foot after heel strike (foot slap) and dragging of the toe during swing (toe drag). At heel strike, the foot generally falls uncontrolled to the ground, producing a distinctive slapping noise (foot slap). During mid-swing, toe drag prevents proper limb advancement and increases the risk of tripping. A conventional approach to the treatment of anterior/posterior compartment leg weakness is a mechanical brace called an Ankle Foot Orthosis (AFO). Although AFOs may offer some biomechanical benefits, disadvantages still remain. W. E. Carlson, C. L. Vaughar, D. L. Damiano, and M. F. Abel, “Orthotic Management of Gait in Spastic Diplegia,” American Journal of Physical Medicine & Rehabilitation, vol. 76, pp. 219-225, 1997, found that AFOs did not improve gait velocity or stride length in children with cerebral palsy. Still further, J. F. Lehmann, S. M. Condon, B. J. de Lateur, and R. Price, “Gait Abnormalities in Peroneal Nerve Paralysis and Their Corrections by Orthoses: A Biomechanical Study,” Archives of Physical Medicine and Rehabilitation, vol. 67, pp. 380-386, 1986 June, discovered that although a constant stiffness AFO was able to provide safe toe clearance in drop-foot patients, the device did not reduce the occurrence of slap foot.
Moreover, the passive devices typically do not address a dominant complication of posterior muscle weakness i.e., the lack of late stance powered plantar flexion. Since terminal stance powered plantar flexion is paramount for limiting heel strike losses of the adjacent leg, a patient with weak posterior muscles will likely experience an increase in impact force on the leading leg at heel strike and, consequently, an increase in the metabolic rate of walking. Therefore, there is a need for improved systems and methods of permanent assistive devices for the treatment of lower-extremity pathology.